Known automated systems for picking and stacking material, such as print media, use a vacuum cup to pick the material and then displace the cup and media to stack the material in a different location. However, at times the cup fails to pick up the required material or the required material is dropped during transit to the stacking location. As a result, the stacked material is incomplete and unsuitable for use. The known systems do not have a means for determining that stacked material is missing material that failed to be transported to the stacking location.